Two-dimensional position sensor

ABSTRACT

A two-dimensional position sensor is formed by drive electrodes ( 52 ) and sense electrodes ( 62, 64, 66 ) both extending in the x-direction and interleaved in the y-direction. The sense electrodes comprise several groups, two of which co-extend in the x-direction over each different portions of extent in the x-direction. The drive and sense electrodes are additionally arranged to capacitively couple with each other. In use, drive signals are applied to the drive electrodes and then the resultant sense signals received from the sense electrodes measured. The position of a touch or stylus actuation on the sensor is determined in the x- and y-directions as follows. In the x-direction, the position is determined by an interpolation between sense signals obtained from co-extending pairs of sense electrodes, and in the y-direction by interpolation between sense signals obtained from different sequences of drive signals applied to the drive electrodes.

BACKGROUND OF THE INVENTION

The invention relates to 2-dimensional position sensors. Moreparticularly the invention relates to 2-dimensional position sensors ofthe type based on capacitive proximity sensing techniques. Such sensorsmay be referred to as 2-dimensional capacitive transducing (2DCT)sensors. 2DCT sensors are based on detecting a disturbance in acapacitive coupling of sensor electrodes, either to ground or to anotherelectrode, caused by the proximity of a pointing object. A measuredlocation for the disturbance corresponds to a measured position for thepointing object.

2DCT sensors are typically actuated by a human finger, or a stylus.Example devices include touch screen and touch sensitivekeyboards/keypads, e.g. as used for controlling consumer electronicdevices/domestic appliances, and possibly in conjunction with anunderlying display, such as a liquid crystal display (LCD), or cathoderay tube (CRT). Other devices which may incorporate 2DCT sensors includepen-input tablets and encoders used in machinery for feedback controlpurposes, for example. 2DCT sensors are capable of reporting at least a2-dimensional coordinate, Cartesian or otherwise, related to thelocation of an object or human body part, by means of a capacitancesensing mechanism.

Devices employing 2DCT sensors have become increasingly popular andcommon, not only in conjunction with personal computers, but also in allmanner of other appliances such as personal digital assistants (PDAs),point of sale (POS) terminals, electronic information and ticketingkiosks, kitchen appliances and the like. 2DCT sensors are frequentlypreferred to mechanical switches for a number of reasons. For example,2DCT sensors require no moving parts and so are less prone to wear thantheir mechanical counterparts. 2DCT sensors can also be made inrelatively small sizes so that correspondingly small, and tightly packedkeypad arrays can be provided. Furthermore, 2DCT sensors can be providedbeneath an environmentally sealed outer surface/cover panel. This makestheir use in wet environments, or where there is a danger of dirt orfluids entering a device being controlled attractive. Furthermore still,manufacturers often prefer to employ interfaces based on 2DCT sensors intheir products because such interfaces are often considered by consumersto be more aesthetically pleasing than conventional mechanical inputmechanisms (e.g. pushbuttons).

U.S. Pat. No. 5,730,165 describes a capacitive sensing device whichrelies on measuring the capacitance of a sensing electrode to a systemreference potential (earth). The principles described in U.S. Pat. No.5,730,165 utilize passive capacitive sensing techniques. The contents ofU.S. Pat. No. 5,730,165 are incorporated herein in their entirety byreference as background material to the invention. In broad summary,passive capacitive sensors employ sensing electrodes coupled tocapacitance measurement circuits. Each capacitance measurement circuitmeasures the capacitance (capacitive coupling) of its associated sensingelectrode to a system ground. When there is no pointing object near tothe sensing electrode, the measured capacitance has abackground/quiescent value. This value depends on the geometry andlayout of the sensing electrode and the connection leads to it, and soon, as well as the nature and location of neighbouring objects, e.g. thesensing electrodes proximity to nearby ground planes. When a pointingobject, e.g. a user's finger, approaches the sensing electrode, thepointing object appears a virtual ground. This serves to increase themeasured capacitance of the sensing electrode to ground. Thus anincrease in measured capacitance is taken to indicate the presence of apointing object.

U.S. Pat. No. 5,730,165 are primarily directed to discrete (singlebutton) measurements, and not to 2D position sensor applications.However the principles described in U.S. Pat. No. 5,730,165 are readilyapplicable to 2DCT sensors, e.g. by providing electrodes to defineeither a 2D array of discrete sensing areas, or rows and columns ofelectrodes in a matrix configuration.

U.S. Provisional Patent Application 60/803,510, subsequently filed asU.S. patent application Ser. No. 11/752,615 which published asUS2006/0279395 on 6 Dec. 2007, describes a 2DCT sensor comprising asubstrate with a sensitive area defined by a pattern of electrodes inwhich the electrodes are sensed by passive sensing techniques. Acapacitance measurement circuit of the type described in U.S. Pat. No.6,288,707, as shown in FIG. 5 of U.S. application 60/803,510, is coupledto the sensing electrodes for determining a change in capacitance causedby the approach of a user's finger or other object to the sensingelectrodes. Further details of sensor circuitry and methods of drivingthe sensor circuitry are available in U.S. Pat. No. 5,730,165 and U.S.Pat. No. 7,148,704. It has been found that there are some limitationsassociated with 2DCT sensors which operate on passive sensingtechniques. For example, passive 2DCT sensors are strongly sensitive toexternal ground loading. That is to say, the sensitivity of such sensorscan be significantly reduced by the presence of nearby low impedanceconnections to ground which can limit their applicability. For example,some types of display screen technology provide for a low-impedancecoupling to ground across the visible screen. This means a passive 2DCToverlaying the display screen will often under-perform because therelatively strong coupling to ground through the screen itself reducesthe sensitivity of the 2DCT to any additional coupling to ground causedby an approaching pointing object. A similar effect means 2DCT sensorscan be relatively sensitive to changes in their environment e.g., a 2DCTsensor might behave differently according to its location because ofdifferences in capacitive coupling (ground loading) to external objects.2DCT sensors are also relatively sensitive to environmental conditions,such as temperature, humidity, accumulated dirt and spilt fluids, etc.All of these effect the sensor's reliability and sensitivity.Furthermore, the measurement circuitry associated with passive 2DCTsensing is generally of high input impedance. This makes passive sensorsprone to electrical noise pick up, e.g. radio frequency (RF) noise. Thiscan reduce reliability/sensitivity of the sensor and also placesconstraints on sensor design (e.g. there is limited freedom to userelatively long connection leads/traces between the sensing electrodesand associated circuitry.

Thus, there is a need to develop an improved 2DCT sensor which addressesthe above-mentioned problems of certain known 2DCT sensors andparticularly those 2DCT sensors which rely on passive capacitive sensingtechniques as described in U.S. application 60/803, 510.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided atwo-dimensional position sensor comprising a substrate with a sensitivearea defined by a pattern of electrodes, the pattern of electrodesincluding drive electrodes and sense electrodes generally extending in afirst direction (hereinafter, the x-direction) and interleaved in asecond direction (hereinafter, the y-direction, where the x- andy-directions can be oriented along any axis of actuation, but aregenerally orthogonally oriented towards each other), wherein the senseelectrodes comprise first, second and third groups of elements shapedsuch that adjacent ones of the elements of the first and second groupsco-extend in the x-direction over a portion of the sensitive area andadjacent ones of the elements of the second and third groups co-extendin the x-direction over another portion, and wherein the driveelectrodes are arranged to capacitively couple with the senseelectrodes.

The 2DCT sensor of the invention uses active capacitive sensing. Active2DCT sensors have been found to be less prone to the above-mentionedeffects associated with passive 2DCT sensors. The active 2DCT sensor ofthe invention is based on measuring capacitive coupling between twoelectrodes rather than between a single sensing electrode and a systemground. The principles underlying active capacitive sensing techniquesare described in U.S. Pat. No. 6,452,514, the contents of which areincorporated herein by reference. In an active-type sensor, oneelectrode, the so-called drive electrode, is supplied with anoscillating drive signal. The degree of capacitive coupling of the drivesignal to the sense electrode(s) is determined by measuring the amountof charge transferred to the sense electrode by the oscillating drivesignal. The amount of charge transferred, i.e. the strength of thesignal seen at the sense electrode, is a measure of the capacitivecoupling between the electrodes. When there is no pointing object nearto the electrodes, the measured signal on the sense electrode has abackground/quiescent value. However, when a pointing object, e.g. auser's finger, approaches the electrodes (or more particularlyapproaches near to the region separating the electrodes), the pointingobject acts as a virtual ground and sinks some of the drive signal(charge) from the drive electrode. This acts to reduce the strength ofthe component of the drive signal coupled to the sense electrode. Thus adecrease in measured signal on the sense electrode is taken to indicatethe presence of a pointing object.

An active sensor described in U.S. Pat. No. 6,452,514 comprises driveelectrodes extending in rows on one side of a substrate and senseelectrodes extending in columns on the other side of the substrate so asto define an array of N by M touch keys. Each key corresponds to anintersection between a drive electrode and a sense electrode. Thus thearray of keys described in U.S. Pat. No. 6,452,514 may be termed amatrixed array with a single drive electrode associated with keys in agiven row and a single sense electrode associated with keys in a givencolumn. This reduces the number of drive and sense channels required,since a single drive channel simultaneously drives all of the keys in agiven row and a single sense channel senses all of the keys in a givencolumn. The capacitive coupling between the electrodes at the positionsof the different keys can be determined by driving the appropriate rowand sensing the appropriate column. For example, to determine thecapacitive coupling between the electrodes associated with a key at theintersection of row 2 and column 3, the drive signal is applied to thedrive electrode of row 2 while the sense channel associated with thesense electrode of column 3 is active. The output from the active sensechannel reflects the capacitive coupling between the electrodesassociated with the key under investigation. Different keys can bescanned by sequencing through different combinations of drive and sensechannels. In one mode the drive electrodes may be driven sequentiallywhile the sense electrodes are all continuously monitored. A signalchange on one (or more) of the sense electrodes indicates the presenceof a pointing object. The sense electrode on which the change is seendefines position in one dimension, the drive electrode being driven whenthe change was seen defines position in the other dimension.

When implementing drive and sense channel circuitry of the kinddescribed in U.S. Pat. No. 6,452,514 in an integrated circuit (IC) chippackage, each drive channel requires one pin-out while each sensechannel requires two pin-outs. Thus, for a 2DCT sensor according to theinvention comprising an array of n×m sensing areas, a matrixed arrayrequires N+2M pin-outs (or M+2N pin-outs depending on which of the rowsand columns are drive or sense electrodes). However, a discrete(non-matrixed array) requires 3 NM pin-outs. Circuit connections, and inparticular pin-outs in IC chip implementations, are expensive, both inmonetary terms, and in terms of the physical space and complexityrequired to implement them. Advantageously, the 2DCT sensor of theinvention requires only one pin-out for each drive channel and twopin-outs for each sense channel.

The sensor may preferably further comprise a controller comprising adrive unit for applying drive signals to the drive (D) electrodes, and asense unit for measuring sense signals received from the sense (S)electrodes representing a degree of coupling of the drive signalsbetween the drive electrodes and the sense electrodes. Since sensechannels are generally more expensive to implement that drive channels,a cheaper sensor in accordance with the invention can be provided whichmay employ a controller implemented in an integrated chip requiringfewer pin-outs than known matrixed passive capacitive position sensors.

The controller may preferably further comprise a processing unit forcalculating a position for an interacting object from an analysis of thesense signals obtained by applying drive signals to the driveelectrodes. The position determination in each axis may includeinterpolating so that position can be determined. Namely, the processingunit is preferably operable to determine position in the x-direction byan interpolation between sense signals obtained from co-extending pairsof groups of sense electrodes, and position in the y-direction by aninterpolation between sense signals obtained from different sequences ofdrive signals applied to the drive electrodes.

The electrodes can be made of a transparent material, such as indium tinoxide (ITO), Orgacon™ or any other suitable material. The substrate canalso be made of a transparent material, such as glass or a transparentplastics material, e.g. a polymethyl methacrylate (PMMA) such asPerspex, Polyethylene Terephthalate (PET), a polycarbonate (PC) such asLexan™, or a cycloolefin copolymer (COP) such as Zeonor™ or Topas™.However, in some applications, it may be the case that the electrodesand/or the substrate are opaque e.g. metal electrodes on opaque plastic,to create a mouse pad or track pad for example.

The groups of sense electrodes which co-extend can have complementarytapers over their distance of co-extension to provide ratiometriccapacitive signals. Alternatively, the elements of respective groups ofsense electrodes which co-extend have adjacent blocks of varying areaover their distance of co-extension to provide ratiometric capacitivesignals. The sense electrodes may be structured in a variety oftopographical forms in order to provide the co-extension. For example,the drive and sense electrodes may interdigitate in order to providesaid capacitive coupling. Over the sensitive area, the drive and senseelectrodes are advantageously formed of conductive material which doesnot exceed a feature width substantially smaller than a characteristicspacing in the y-direction between adjacent rows of drive electrodes,such as 2, 3, 4, 5, 6, 7, 8, 9 or 10 times smaller. This keeps theamount of conductive material low while providing a large amount ofcapacitive coupling, which has benefits for noise reduction and signalstrength.

In preferred embodiments, the elements of at least one of the first andthird groups of sense electrodes form two sections separated in they-direction by a channel, and wherein the elements of the second groupof sense electrodes are externally connected to the sense unit throughconductive traces that pass through the channels to a side of thesensitive area. This type of arrangement, which can also be applied tofurther groups of sense electrodes if provided, ensures that theconductive traces leading to inner ones of the sense electrode groups donot pass between paired drive and sense electrodes of peripheral ones ofthe sense electrode groups. The reduction in their capacitive couplingthat would otherwise occur is thus avoided.

If there are at least three groups of sense electrodes externallyconnected to the sense unit through one side of the sensitive area,referred to as peripheral, intermediate and inner sense electrodes, itis advantageous if the elements of the inner sense electrodes areexternally connected to the sense unit through conductive traces whichbecome progressively wider in the y-direction from said one side towardsthe elements of the inner sense electrodes. This reduces the resistanceof the path to the inner sense electrode groups and avoids reduction insensitivity for such groups. For example, the elements of the peripheraland intermediate sense electrodes can form two sections separated in they-direction, wherein the two sections of each element of theintermediate sense electrodes are externally connected to the sense unitthrough respective conductive traces that pass between the two sectionsof the peripheral sense electrodes to said one side of the sensitivearea and leave a channel therebetween, and wherein the elements of theinner sense electrodes are externally connected to the sense unitthrough conductive traces that pass through the channel formed betweenthe sections of the peripheral and intermediate sense electrodes.

It can also be advantageous if the elements of at least one of thegroups of sense electrodes are hollow in the plane of the sensitivearea. This is one way of reducing conductive material which does notcontribute significantly to capacitive coupling with the driveelectrodes. Other measures are also possible, such as throughinterdigitation and use of line-based electrode forms having a smallfeature width as referred to above.

It will be understood that the position of an object is defined by anappropriate coordinate system, most commonly an xy Cartesian system inwhich they are orthogonal, although they may be at a non-orthogonalangle. Moreover, in the following there is reference to x- or horizontaland y- and vertical respectively for convenience, although this impliesno particular alignment to real space, such as relative to the directionof gravity.

According to a second aspect of the invention there is provided acontrol panel incorporating a two-dimensional position sensor accordingto the first aspect of the invention.

According to a third aspect of the invention there is provided anapparatus having a control panel incorporating a two-dimensionalposition sensor according to the first aspect of the invention.

According to a fourth aspect of the invention there is provided a methodof sensing position of an actuation on a sensitive area of atwo-dimensional position sensor, the sensitive area being defined by apattern of electrodes including drive electrodes and sense electrodes,both generally extending in a first direction, hereinafter thex-direction, and interleaved in a second direction, hereinafter they-direction, wherein the sense electrodes comprise first, second andthird groups of elements shaped such that adjacent ones of the elementsof the first and second groups co-extend in the x-direction over aportion of the sensitive area and adjacent ones of the elements of thesecond and third groups co-extend in the x-direction over anotherportion, and wherein the drive electrodes are arranged to capacitivelycouple with the sense electrodes, the method comprising: applying drivesignals to the drive electrodes; measuring sense signals received fromeach group of the sense electrodes representing a degree of capacitivecoupling of the drive signals between the drive electrodes and eachgroup of the sense electrodes; determining position in the x-directionby an interpolation between sense signals obtained from co-extendingpairs of groups of sense electrodes; and determining position in they-direction by an interpolation between sense signals obtained fromdifferent sequences of drive signals applied to the drive electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how the same maybe carried into effect reference is now made by way of example to theaccompanying drawings.

FIG. 1 is a view of a front side of a position sensor according to anembodiment of the invention.

FIG. 1A shows how the drive electrodes of FIG. 1 are coupled via drivechannels to drive units within the main drive unit of the controller ofthe sensor.

FIG. 1B is a schematic exploded view of a part of the electrode patternof FIG. 1.

FIG. 1C schematically shows a circuit which may be used to measure thecharge transferred from a driven one of the drive electrodes to thesense electrodes.

FIG. 1D shows schematically the timing relationships of operation of thecircuit of FIG. 1C.

FIG. 1E shows schematically the drive signal timings suitable for usewith the position sensor of FIG. 1.

FIGS. 2 to 12 show further electrode patterns for position sensorsembodying the invention.

FIG. 13 shows a still further sensor embodying the invention.

FIGS. 14, 14A and 14B show a still further embodiment of a sensor devicewith FIG. 14 showing the full electrode pattern, FIG. 14A only one rowof the sense electrodes and FIG. 14B only the drive electrodes.

FIGS. 15 and 15A show a still further embodiment of a sensor device

FIGS. 16 and 16A show a still further embodiment of a sensor deviceFIGS. 15-18 show still further sensors embodying the invention.

FIG. 17 shows a still further sensor embodying the invention.

FIG. 18 shows a still further sensor embodying the invention.

FIG. 19 schematically shows a portable personal computer incorporating asensor according to an embodiment of the invention.

FIG. 20 schematically shows a washing machine incorporating a sensoraccording to an embodiment of the invention.

FIG. 21 schematically shows a cellular telephone incorporating a sensoraccording to an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 is a view of a front side of a position sensor 10 according to anembodiment of the invention. The front side of the position sensor istypically the side facing the user during normal use of the sensor or anapparatus incorporating the sensor. The sensor 10 comprises a substrate40 bearing an electrode pattern 30 defining a sensitive area of thesensor and a controller 20. The controller 20 is coupled to electrodeswithin the electrode pattern by a connection 24. The electrode patternis on one side of the substrate, typically on the opposite side of thesubstrate from the side facing the user during normal use.

The electrode pattern 30 on the substrate 40 can be provided usingconventional techniques (e.g. lithography, deposition, or etch ordeactivation techniques). The substrate is of a dielectric material suchas a plastics film, in this case Polyethylene Terephthalate (PET). Theelectrodes comprising the electrode pattern are of a transparentconductive material, in this case Indium Tin Oxide (ITO). Alternatively,the electrodes could be formed from an opaque conductive material suchas metal e.g. copper. The substrate may be bonded to an overlying panel(not shown) using a suitable pressure sensitive adhesive (PSA) which canbe clear to allow light transmission. Thus the sensitive area of thesensor as a whole is transparent. If transparent, the sensor layer maybe used over an underlying display without obscuration. In otherembodiments, if the sensor layer is opaque, it may comprise aconventional printed circuit board or other substrate with a copperelectrode pattern, e.g. for use in a mobile telephone keypad.

The controller 20 provides the functionality of a drive unit 12 forsupplying drive signals to portions of the electrode pattern 30, a senseunit 14 for sensing signals from other portions of the electrode pattern30, and a processing unit 16 for calculating a position based on thedifferent sense signals seen for drive signals applied to differentportions of the electrode pattern. The controller 20 thus controls theoperation of the drive and sense units, and the processing of responsesfrom the sense unit 14 in the processing unit 16, in order to determinethe position of an object, e.g. a finger or stylus, adjacent the sensor10. The drive unit 12, sense unit 14 and processing unit 16 are shownschematically in FIG. 1 as separate elements within the controller.However, in general the functionality of all these elements will beprovided by a single integrated circuit chip, for example a suitablyprogrammed general purpose microprocessor, or field programmable gatearray, or an application specific integrated circuit.

Referring to FIG. 1, the electrodes 52 are drive (D) electrodesrepresented by longitudinal bars extending in the x-direction. Adjacentdrive electrodes 52 are spaced apart by three groups 62, 64, 66 of sense(S) electrodes.

FIG. 1A shows how the drive electrodes 52 are coupled via drive channelsD₁, D₂, D₃, D₄, D₅, D₆, D₇, D₈ to respective drive units DD₁, DD₂, DD₃,DD₄, DD₅, DD₆, DD₇, DD₈ within the main drive unit of the controller 20of the sensor. In this example, a separate drive unit is provided foreach drive channel, although a single drive unit with appropriatemultiplexing may also be used. Each drive channel supplies drive signalsto a group of three drive electrodes 52, except for either D₁ or D₈which supplies one drive electrode. The drive electrodes 52 are eachconnected to each other by a chain or row of resistors 70.Alternatively, a single resistive strip could be used. The drivechannels are controlled by the controller 20 to apply drive signals tothe respective electrodes. The three groups of sense electrodes 62, 64,66 are each respectively coupled via a sense or receive channels S₁, S₂,S₃ to the sense unit 14 of the controller 20, as shown in FIG. 1A. Thesense channels are also controlled by the controller 20 to receivesignals from the respective sense electrodes.

FIG. 1B is a schematic exploded view of a part of the electrode patternof FIG. 1. It is noted that each central sense electrode 64 is connectedto the external circuit connection S₂ via a conductive trace orfeed-through 65 that divides the adjacent side sense electrode 66 intotwo portions 66A and 66B separated by a channel. This arrangement isadvantageous compared to the alternative arrangements such as shown inFIG. 18 below, which reproduces FIG. 11 of co-pending U.S. PatentApplication 60/803,510, since it avoids the feed-through to the centralelectrode passing between the side sense electrode and one of theadjacent drive electrodes, which in designs of the type shown in FIG. 11has the effect or reducing the interaction between the drive electrodeand the affected sense electrode. Feed-through connections to one ormore groups of sense electrodes are thus arranged to subdivide anothergroup of sense electrodes to avoid the feed-through connections lyingdirectly adjacent to any of the drive electrodes. This approach can beused in a wide variety of electrode patterns so that feed-throughconnections to one group of sense electrodes do not pass between driveelectrodes and another group of sense electrodes with which the driveelectrode is paired.

As shown in FIGS. 1, 1A and 1B, the sense electrodes are classified intothree groups. A first group of tapered electrodes 62 is arranged at theleft hand side of the sensitive area of the electrode pattern. Thetapered electrodes 62 are cut into two sections 62A and 62B defining achannel therebetween. A second group of triangular electrodes 64 withdouble tapers is arranged so that the electrodes extend inwards fromthen left and right hand sides respectively of the sensitive areatowards the centre. A third group of tapered electrodes 66 is arrangedat the right hand side of the sensitive area of the electrode pattern.The tapered electrodes 66 are cut in two sections 66A and 66B defining achannel therebetween. The first and second groups of electrodesco-extend over a portion of the extent in the x-direction, labelledregion I in FIG. 1B, and the second and third groups co-extend overregion II. The different regions provide ratiometric capacitive signalsindicative of capacitive coupling of a user's finger on a part of thesensor where sense electrodes are present. Advantageously, a user'sfinger approaching the sensor is sensed by two different electrodegroups to provide a beneficial mixing of signals and hence determine thex-position of a finger or other object on the sensor. As previouslymentioned, the first and third groups of sense electrodes are cutrespectively into two sections to define channels therebetween. Thechannel between left hand side electrodes 62A and 62B has a conductivetrace 63 from second group electrode 64 passing therethrough whichterminates near to the left hand side perimeter of the sensitive area.The conductive traces 63 have no function other than to provide symmetrywith the conductive traces 65 which serve as feed-throughs to the sensechannels. Namely, each channel between the right hand side electrodes66A and 66B allows a conductive trace 65 from the second group 64 topass therethrough and couple to sense channel S₂.

As shown in FIG. 1B, each drive bar electrode 52 is connected to itsvertically adjacent bar or bars by an electrically conductive line witha discrete resistor 70 in series with it. The drive electrodes areexternally connected via conductive traces to drive channels D₁-D₈ fromrespective drive unit(s) in the controller. In FIGS. 1, 1A, 1B, thedrive channels D₁-D₈ are shown connected to every third drive electrode,i.e. each drive channel drives a group of three electrodes 52.

The sensor 10 of the invention therefore comprises a plurality of drivenelectrodes and a plurality of sense electrodes comprising a network ofinterconnected electrodes across the sensitive area of the sensor. Eachneighbouring pairing of a drive element and a sense element may beconsidered to correspond to a discrete sensor area which may be operatedaccording to the techniques described in U.S. Pat. No. 6,452,514. Inuse, the position of an object is determined in a measurementacquisition cycle in which the bar electrodes 52 are sequentially drivenby respective drive channels and the amount of charge transferred to thesense electrodes from each bar electrode is determined by the sensechannels.

FIG. 1C schematically shows a circuit which may be used to measure thecharge transferred from a driven one of the drive electrodes to thesense electrodes, the drive electrode being driven at a given time andthe sense electrode have a self capacitance. This is determinedprimarily by their geometries, particularly in the regions where theyare at their closest. Thus the driven drive electrode is schematicallyshown as a first plate 100 of a capacitor 105 and the sense electrode isschematically shown as a second plate 104 of the capacitor 105.Circuitry of the type shown in FIG. 1C is more fully described in U.S.Pat. No. 6,452,514. The circuit is based in part on the charge-transfer(“QT”) apparatus and methods disclosed in U.S. Pat. No. 5,730,165, thecontents of which are, as noted above, herein incorporated by reference.

The drive channel associated with the presently driven electrode 100,the sense channel associated with sense electrode 104 and elements ofthe sensor controller are shown as combined processing circuitry 400 inFIG. 1C. The processing circuitry 400 comprises a sampling switch 401, acharge integrator 402 (shown here as a simple capacitor), an amplifier403 and a reset switch 404, and may also comprise optional chargecancellation means 405.

FIG. 1D shows schematically the timing relationships between the drivenelectrode drive signal from the drive channel 101 and the sample timingof switch 401. The drive channel 101 and the sampling switch 401 areprovided with a suitable synchronizing means, which may be amicroprocessor or other digital controller 408, to maintain thisrelationship. In the implementation shown, the reset switch 404 isinitially closed in order to reset the charge integrator 402 to a knowninitial state (e.g., zero volts). The reset switch 404 is then opened,and at some time thereafter the sampling switch 401 is connected tocharge integrator 402 via terminal 1 of the switch for an intervalduring which the drive channel 101 emits a positive transition, andthereafter reconnects to terminal 0, which is an electrical ground orother suitable reference potential. The drive channel 101 then returnsto ground, and the process repeats again for a total of ‘n’ cycles,(where n may be 1 (i.e. 0 repeats), 2 (1 repeat), 3 (2 repeats) and soon). It can be helpful if the drive signal does not return to groundbefore the charge integrator is disconnected from the sense electrodesince otherwise an equal and opposite charge would flow into/out of thesense channel during positive and negative going edges, thus leading tono net transfer or charge into the charge detector. Following thedesired number of cycles, the sampling switch 401 is held at position 0while the voltage on the charge integrator 402 is measured by ameasurement means 407, which may comprise an amplifier, ADC or othercircuitry as may be appropriate to the application at hand. After themeasurement is taken, the reset switch 404 is closed again, and thecycle is restarted, though with the next drive channel and drivenelectrode in sequence replacing the drive channel 101 and drivenelectrode 100 schematically shown in FIG. 1C. The process of making ameasurement for a given driven electrode is referred to here as being ameasurement ‘burst’ of length ‘n’ where ‘n’ can range from 1 to anyfinite number. The circuit's sensitivity is directly related to ‘n’ andinversely to the value of the charge integrator 402.

It will be understood that the circuit element designated as 402provides a charge integration function that may also be accomplished byother means, and that this type of circuit is not limited to the use ofa ground-referenced capacitor as shown by 402. It should also beself-evident that the charge integrator 402 can be an operationalamplifier based integrator to integrate the charge flowing through inthe sense circuitry. Such integrators also use capacitors to store thecharge. It may be noted that although integrators add circuit complexitythey provide a more ideal summing junction load for the sense currentsand more dynamic range. If a slow speed integrator is employed, it maybe necessary to use a separate capacitor in the position of 402 totemporarily store the charge at high speed until the integrator canabsorb it in due time, but the value of such a capacitor becomesrelatively non-critical compared to the value of the integrationcapacitor incorporated into the operational amplifier based integrator.

It can be helpful for the sampling switch 401 to connect the senseelectrode of the sensor to ground when not connected to the chargeintegrator 402 during the changes of drive signal of the chosen polarity(in this case positive going). This is because this can create anartificial ground plane, thus reducing RF emissions, and also, as notedabove, permitting the coupled charge of opposite polarity to that beingsensed by the charge integrator 402 to properly dissipate andneutralize. It is also possible to use a resistor to ground on the senseelectrode to accomplish the same effect between transitions of drivechannels 101. As an alternative to a single-pole double-throw (SPDT)switch 401, two independent switches can be used if timed in anappropriate manner.

As described in U.S. Pat. No. 5,730,165, there are many signalprocessing options possible for the manipulation and determination of adetection or measurement of signal amplitude. U.S. Pat. No. 5,730,165also describes the gain relationship of the arrangement depicted in FIG.1C, albeit in terms of a single electrode system. The gain relationshipin the present case is the same. The utility of a signal cancellationmeans 405 is described in U.S. Pat. No. 4,879,461, as well as in U.S.Pat. No. 5,730,165. The disclosure of U.S. Pat. No. 4,879,461 is hereinincorporated by reference. The purpose of signal cancellation is toreduce the voltage (i.e. charge) build-up on the charge integrator 402concurrently with the generation of each burst (positive goingtransition of the drive channel), so as to permit a higher couplingbetween the driven electrodes and the receiving sense electrodes. Onebenefit of this approach is to allow a large sensing area that issensitive to small deviations in coupling between the electrodes atrelatively low cost. Such large sense couplings are present inphysically relatively large electrodes such as might be used in humantouch sensing pads. Charge cancellation permits measurement of theamount of coupling with greater linearity, because linearity isdependent on the ability of the coupled charge from the driven electrode100 to the sense electrode 104 to be sunk into a ‘virtual ground’ nodeover the course of a burst. If the voltage on the charge integrator 402were allowed to rise appreciably during the course of a burst, thevoltage would rise in inverse exponential fashion. This exponentialcomponent has a deleterious effect on linearity and hence on availabledynamic range.

The drive channel may be a simple CMOS logic gate powered from aconventionally regulated supply and controlled by the sensor controller20 to provide a periodic plurality of voltage pulses of a selectedduration (or in a simple implementation a single transition fromlow-to-high or high-to-low voltage, i.e. a burst of one pulse).Alternatively, the drive channel may comprise a sinusoidal generator orgenerator of a cyclical voltage having another suitable waveform. Achanging electric field is thus generated on the rising and failingedges of the train of voltage cycles applied to the driven electrode.The driven electrode and the sense electrode are assumed to act asopposing plates of a capacitor having a capacitance C_(E). Because thesense electrode is capacitively coupled to the driven electrode, itreceives or sinks the changing electric field generated by the drivencolumn electrode. This results in a current flow in the sense electrodeinduced by the changing voltage on the driven electrode throughcapacitive differentiation of the changing electric fields. The currentwill flow towards (or from, depending on polarity) the sense channels inthe sense unit 14. As noted above, the sense channel may comprise acharge measurement circuit configured to measure the flow of chargeinto/out of (depending on polarity) the sense channel caused by thecurrents induced in the sense electrode.

The capacitive differentiation occurs through the equation governingcurrent flow through a capacitor, namely:

$I_{E} = {C_{E} \times \frac{\mathbb{d}V}{\mathbb{d}t}}$where I_(E) is the instantaneous current flowing to the sense channel Sand dV/dt is the rate of change of voltage applies to the drivenelectrode D₁. The amount of charge coupled to the sense electrode (andso into/out of the sense channel S) during an edge transition is theintegral of the above equation over time, i.e.Q _(E) =C _(E) ×V.

The charge coupled on each transition, Q_(E), is independent of the risetime of V (i.e. dV/dt) and depends only on the voltage swing at thedriven electrode (which may readily be fixed) and the magnitude of thecoupling capacitance C_(E) between the driven electrode and senseelectrode. Thus a determination of the charge coupled into/out of chargedetector comprising the sense channel in response to changes in thedrive signal applied to the driven electrode is a measure of thecoupling capacitance C_(E) between the driven electrode and the senseelectrode.

The capacitance of a conventional parallel plate capacitor is almostindependent of the electrical properties of the region outside of thespace between the plates (at least for plates that are large in extentcompared to their separation). However, for a capacitor comprisingneighbouring electrodes in a plane this is not the case. This is becauseat least some of the electric fields connecting between the drivenelectrode and the sense electrode “spill” out from the substrate. Thismeans the capacitive coupling (i.e. the magnitude of C_(E)) between thedriven electrode and the sense electrode is to some extent sensitive tothe electrical properties of the region in the vicinity of theelectrodes in to which the “spilled” electric field extends.

In the absence of any adjacent objects, the magnitude of C_(E) isdetermined primarily by the geometry of the electrodes, and thethickness and dielectric constant of the sensor substrate. However, ifan object is present in the region into which the electric field spillsoutside of the substrate, the electric field in this region may bemodified by the electrical properties of the object. This causes thecapacitive coupling between the electrodes to change, and thus themeasured charge coupled into/from the charge detector comprising thesense channel(s) changes. For example, if a user places a finger in theregion of space occupied by some of the of the spilled electric fields,the capacitive coupling of charge between the electrodes will be reducedbecause the user will have a substantial capacitance to ground (or othernearby structures whose path will complete to the ground referencepotential of the circuitry controlling the sense elements). This reducedcoupling occurs because the spilled electric field which is normallycoupled between the driven electrode and sense electrode is in partdiverted away from the electrode to earth. This is because the objectadjacent the sensor acts to shunt electric fields away from the directcoupling between the electrodes.

Thus, by monitoring the amount of charge coupled between the drivenelectrode and the sense electrode, changes in the amount of chargecoupled between them can be identified and used to determine if anobject is adjacent the sensor (i.e. whether the electrical properties ofthe region into which the spilled electric fields extend have changed).

The two-dimensional position sensor or touch screen sensor of theinvention therefore relies on active capacitive sensing techniques asopposed to passive capacitive sensing techniques which provides for amore optimal determination of position of an object, greater linearityof output signal as an object moves over the sensor, and greatersensitivity of the sensor to capacitive changes caused by an approachingobject. In addition, as previously described, the sensor of theinvention is more versatile and less affected by ground loading comparedto known sensors.

As previously described, the sensor of the invention operates on matrixsensing principles described in U.S. Pat. No. 6,452,514. Such matrixsensing involves capacitive field changes between two electrodes, adrive electrode and a sense electrode, rather than determination of achange in capacitance from a sensing electrode to a reference potential(e.g. ground). Such matrix sensing in the touch screen sensor of theinvention involves capacitive e-fields which are more “closed” comparedto capacitive e-fields in passive sensors which are typically more“open”. This improves the capacitive sensitivity of the sensor.

FIG. 1E shows schematically the drive signal timings suitable for usewith the device of the type shown in FIGS. 1, 1A and 1B. The exampledrive signals assume the device has six drive channels D₁-D₆ with eachdrive channel connecting to every fourth drive electrode 52, therebyleaving two drive electrodes between adjacent drive channel connections,the drive electrodes being connected by a resistive ladder as previouslydescribed. The full sensitive area of the device is sampled by asequence of six drive signals, one for each drive channel. In theillustration, it is assumed that at time t1 a drive voltage V is appliedto channel D₁ with the other channels held at ground. Then at times t2,t3, t4, t5 and t6 the channels D₂ to D₆ respectively are driven with thesame drive voltage V while the other channels are held at ground. Itwill be appreciated that the order of driving is not material, only thata full set of signal data is collected by driving each of the drivechannels. Moreover, the drive voltages are all conveniently the same,but this is also not material. Further, the same effect would beachieved by inverting the illustrated voltages. By virtue of the chainof resistances, e.g. formed by discrete resistors or a thin filmresistive strip, between adjacent drive electrodes, when a given channelis driven with a voltage pulse of magnitude V while the other channelsare grounded, a voltage is dropped from V to zero from the driveelectrode connected to the driven channel through to the nearestgrounded drive channel or channels. In the illustrated example, thevoltage is dropped in thirds, since there are two intermediate driveelectrodes. If there were three intermediate drive electrodes thevoltage would be dropped in quarters and so forth.

The x position of the touch or other actuation is obtained byratiometric interpolation of the signal strength of the two groups ofthe three groups of sense electrodes S₁, S₂, S₃ that have the twostrongest signals.

The y position of the touch or other actuation is also obtained byratiometric interpolation of the signal strength, but in a somewhatdifferent way. Once the full set of 6 signals is collected from the sixdrive events at t1-t6, the two adjacent events that yielded thestrongest signals are selected, and the y position determined byratiometric interpolation of the signal strength of these two signals.For example, if the strongest pair of adjacent signals is obtained fromthe driving of channels D₂ and D₃, and the signal obtained when drivingD₂ is two times greater than the signal obtained when driving D₃, thenthe touch is determined to have taken place ⅓ of the way from the D₂drive electrode towards the D drive electrode.

FIGS. 2, 3, 4 and 5 show further electrode patterns embodying theinvention which can be applied to a substrate incorporated in acapacitive position sensor. The electrode patterns are similar to thepattern of FIG. 1 and identical reference numerals are used to denotethe same features. The bar electrodes 52 are drive (D) electrodes andthe sense (S) electrodes 62, 64, 66 are arranged in three groups. Itwill be noted in FIG. 2 that the electrode pattern comprises first andsecond groups of sense electrodes 62, 64 which are tapered and co-extendtogether in the x-direction in one portion of extent in the x-direction,and the second and third groups of sense electrodes 64, 66 are taperedand co-extend together in another portion of extent in the x-direction.The electrode patterns illustrated in FIGS. 1 to 5 are actual size. Thearrangement of sensor electrodes is important to optimise interaction ofE-fields between the different groups of sensor electrodes and hence todetermine object position accurately. The arrangement of the groups ofsensor electrodes makes it possible for the sensor of the invention tointerpret and determine the position of more than one object approachingthe sensor at the same time. It is possible for the sensor to recognisesimultaneous touches in two different locations on the sense electrodeson separate parts of the sensor provided that the two locations areseparated in the y-direction by at least one, preferably two, drivechannels. Otherwise, the interpolation carried out in the processingunit will conclude that a single touch has taken place at a locationbetween the two simultaneous touches.

FIGS. 6 to 12 illustrate further electrode patterns embodying theinvention. Each sensor has two drive channels D₁, D₂ and three sensechannels S₁, S₂, S₃. Each drive channel supplies drive signals to twodrive electrodes 52. The patterns illustrated in FIGS. 6 to 12 areactual size. All of the sensors comprise three groups of senseelectrodes, except for the sensor of FIG. 6 which comprises four groupsof sense electrodes.

The sensors of the invention may comprise more than three or four groupsof sense electrodes depending on the design of the sensor. Five or moregroups of sense electrodes may be present for example if the width ofthe electrode pattern is increased in the x-direction to accommodate alarger-size capacitive sensor. For example, the sensors described belowand illustrated in FIGS. 14, 15 and 16 each have six groups of senseelectrodes, and the sensor illustrated in FIG. 13 has seven.

FIG. 13 shows an electrode pattern according to another embodiment. Thesubstrate bearing the electrode pattern illustrated in FIG. 13 comprisesan electrode pattern of a larger size in comparison to previousembodiments. The electrode pattern of FIG. 13 has similar features andoperates on the same principles as described in relation to previousembodiments. However, the drive electrodes 52 and the sense electrodes62, 64, 66 comprise projections or teeth which interlock orinterdigitate to form an intricate pattern. The drive electrodes 52comprise teeth, bars or tines of graduating length which project intothe spacings between adjacent teeth of the first, second and thirdgroups of sense electrodes. In the electrode arrangement of FIG. 13, thefirst and third groups of sense electrodes 62, 66 are located on oneside of the drive electrodes (i.e. below each respective driveelectrode) and the second group of sense electrodes is located on theopposite side of the drive electrodes (i.e. above each respective driveelectrode). Therefore, each respective drive electrode 52 is effectively“sandwiched” between the sense electrodes and comprises teeth projectingfrom opposite sides of each respective electrode to inter-engage withspacings between corresponding teeth of the sense electrodes. The driveelectrodes 52 may be described as having a backbone which is arranged ina suitable configuration, for example a V-shaped configuration as shown.Each arm of the V-shaped electrodes are formed with teeth of graduatinglength on each side as previously described. The teeth of the senseelectrodes also have a graduating length to engage optimally with thedrive electrodes.

FIG. 14 shows another embodiment based on similar principles to theembodiment of FIG. 13. To separate out the detail of FIG. 14, FIG. 14Ashows schematically one row of the sense electrodes S₁-S₆, namely theuppermost one, and FIG. 14B shows schematically the six drive electroderows D_(a) to D_(f) which extend in the x-direction, each row beingformed of a sinusoidally extending backbone or spine crossed by parallelteeth, bars or tines extending vertically, i.e. in the y-direction, withthe same vertical extent as each other. Except for at peaks and troughsof the sinusoid, each tine extends through the spine having a portionabove the spine and a portion below the spine. The portions above thespine interdigitate with sense electrodes S₂, S₄ and S₆ arranged abovethe spine and the portions below the spine interdigitate with senseelectrodes S₁, S₃, and S₅ arranged below the spine. The rows of driveelectrodes are arranged in a voltage ladder by means of five resistorsR₁ to R₅ arranged on the left hand side of the illustrated devicebetween the relevant pads as shown schematically in FIG. 14B. It will beunderstood that this device may be driven similarly to as describedabove in relation to the embodiment of FIG. 1, whereby each of D₁ and D₂are driven with a drive voltage while the other one is grounded, and they coordinate of the actuation determined by interpolation between thesense signals obtained from these two drive events. On the right handside of the device, adjacent rows of drive electrodes are connectedwithout a resistor, although one could be connected between each of therelevant pads shown on the right hand side of FIG. 14B if desired. Againas shown in FIG. 14B, there are two drive channels D₁ and D₂ that areconnected to the uppermost and lowermost rows of drive electrodes. Thesense electrodes are formed in 6 groups S₁-S₆ with groups S₁, S₂ and S₃being connected from the left hand side and groups S₄, S₅ and S₆ fromthe right hand side. The groups mutually overlap to provide five rangesof sensing in the x direction that are determined by ratiometricanalysis between the two greatest signals as described above in relationto the embodiment of FIG. 1. It will be understood that this design maybe varied to have different numbers of groups of sense electrodes,different numbers of rows of drive electrodes, different numbers ofdrive channels per drive electrodes (including one) and so forth.

FIG. 15 shows a sensor with associated electrode pattern according to afurther embodiment. There are provided six sensor electrode groups S₁-S₆which overlap in similar manner to previous embodiments in order toallow ratiometric determination of the x location of an actuation. Eachrow of sense electrodes is flanked above and below by a drive electrode52. The special feature of this embodiment, not possessed by previousembodiments, is the stepwise broadening of the feed-through connectionsleading to the innermost sense electrode groups S3 and S4.

FIG. 15A illustrates this feature schematically. The feed-through foreach sense electrode 64 of the group S has three portions ofincrementally increasing width (vertical dimension). The narrowestportion 643 leads from the left-most side of the sensitive area and isflanked by feed-throughs for the sense electrode 66 of the group S₂.Progressing in the positive x-direction, after termination of theshorter upper element 68B of the sense electrode S₁, the feed-throughfor the sense electrode 64 widens into a portion 642, and aftertermination of the longer lower element 68A of the sense electrode S₁,the feed-through widens again into a portion 643. The benefit of theprogressive widening is that the resistance between the innermost senseelectrodes and the sensing circuitry of the associated sense channels isreduced, thereby reducing the effect whereby the innermost senseelectrodes will have less sensitivity than the outer ones.

FIG. 16 shows a sensor with associated electrode pattern according to afurther embodiment which is the same as the embodiment of FIG. 15 exceptthat the conductive material of the innermost sense electrodes arehollowed out.

FIG. 16A illustrates this feature schematically. The illustrated senseelectrode 64 of sense electrode group S₃ is shown hollowed out. All thesense electrodes of sense electrode groups S₃ and S₄ are similarlyhollowed out as evident from FIG. 16. The advantage of this approachcomes from the realisation that in the kind of active sensing usingdriven and sensing electrodes to which the invention relates, the signalis primarily only affected by directly proximal areas of paired driveand sense electrodes. The conductive material in the sense electrodessituated a further distance away from the associated drive electrodesdoes not contribute significantly to the signal and are thereforelargely redundant. Furthermore, it has been established that thisadditional conductive material can contribute significantly to thepick-up of environmental noise. Improved signal-to-noise ratios are thusachieved with the electrode arrangement of FIG. 16 compared with that ofFIG. 15 through the hollowing out of the large central sense electrodes.More rigorously, the design approach to follow is to ensure that thesense electrodes do not extend further than a given distance away fromtheir associated drive electrodes, where the given distance is acharacteristic distance indicative of the sensing depth over which themajority of signal is collected, for example at least 50, 60, 70, 80, 90or 99% of the signal.

FIG. 17 shows a sensor with associated electrode pattern according to afurther embodiment which can be understood with reference to theembodiment of FIG. 15. The electrode pattern is modified in comparisonto the FIG. 15 embodiment in that an additional central spine isinserted to provide an additional sense electrode group of senseelectrodes 69 which are vertically connected to each other and connectedto the associated sense channel by the top of the device rather than thesides. In the illustrated example, discrete bridging componentconnections 71 connect left and right sides of the drive electrodes tobridge over the conductive path between vertically adjacent ones of thesense electrodes 69. This general approach will be understood fromco-pending application 60/803,510 and its subsequent regular filing U.S.Ser. No. 11/752,615 which was published as US2006/0279395 on 6 Dec.2007.

The electrode patterns described in co-pending U.S. Patent Application60/803,510 and its subsequent regular filing U.S. Ser. No. 11/752,615which was published as US2006/0279395 are incorporated herein byreference. The electrode patterns of U.S. Patent Application 60/803,510are similar to the electrode patterns described hereinabove and suchpatterns can be used to measure capacitance based on active capacitivesensing techniques in accordance with the invention described above,although not optimised for such.

FIG. 18 illustrates a pattern of electrodes which is identical to FIG.11 of U.S. Application 60/803,510. The electrode pattern of FIG. 18 canbe applied to a substrate incorporated in a capacitive position sensorembodying the invention. The longitudinal (bar) electrodes 52 are drive(D) electrodes and the electrodes arranged in an interleaved arrangementbetween adjacent drive electrodes are the sense (S) electrodes. Thisembodiment comprises four groups of sense electrodes 62, 64, 66 and 88.The sense electrodes 62, 64, 66 can be connected by conductive traces toreceive channels S₁, S₂, S₃. Likewise, the sense electrode 88 can beconnected a receive channel S₄. The receive channels S₁, S₂, S₃, S₄transmit signals from the sense electrodes to a sensing unit in acontroller. Drive channels D_(x) (not shown) send drive signals togroups of drive electrodes 52. A drive unit in a controller supplies thedrive signals to respective drive electrodes or groups of driveelectrodes. As described in more detail above, a position of an objecton the sensor may be determined by the disruption or reduction ofcapacitive coupling between a drive electrode and one or more senseelectrodes and processing the signals from the sense electrodes tocalculate finger position. The electrode patterns illustrated in FIGS.2, 3, 4 and 6 to 15 of U.S. application 60/803,510 are incorporated byreference herein and form part of the disclosure of this invention. Theembodiments of FIGS. 2, 3, 4 and 6 to 15 of U.S. application 60/803,510are driven and sensed using active (or matrix) capacitive sensing asdescribed in U.S. Pat. No. 6,452,514 and give the advantages asdescribed above.

It will be appreciated that the sensor of the invention is applicable tomany types of device/appliance. For example, sensors can be used withovens, grills, washing machines, tumble-dryers, dish-washers, microwaveovens, food blenders, bread makers, drinks machines, computers, homeaudiovisual equipment, personal computers, portable media players, PDAs,cell phones, computers, games consoles and so forth.

FIG. 19 shows an example of a mobile personal computer (PC) 120. A touchsensor according to the present technique could be used to form part orthe whole of an input control panel of the notebook PC 120. In thefigure, the PC 120 is shown, which includes a display device 122attached to a base 124, which accommodates a processor and othercomponents typically associated with a PC. An input control panel 126includes a keyboard 128. The input control panel 126 further includes atouch sensitive mouse pad 130. The mouse pad can be implemented using atouch sensor according to the present invention. Moreover, the displaydevice 122 can also be implemented with a touch sensor according to thepresent invention overlaid on top of it to provide a touch screen. Thismay be particularly useful for a tablet PC.

FIG. 20 schematically shows a washing machine 91 incorporating a controlpanel 93 which incorporates a sensor according to the invention.

FIG. 21 schematically shows a cellular telephone 95 which mayincorporate one or more sensors according to an embodiment of theinvention. A two-dimensional sensor 98 according to the invention may beused to provide the button panel with buttons 99, or may be a separatesensor co-extensive with the button panel. For example, the button panelmay be retained as a mechanical assembly and the sensor provided toallow drawing, writing or command gestures to be performed by the userover the button panel area, for example to compose text messages inChinese or other Asian characters. The screen 97 may also be overlaidwith a sensor according to the invention.

More generally the invention may be used in conjunction with anyappliance having a human-machine interface. It is also possible toprovide a sensor similar to those described above which is providedseparately from a device/appliance which it may be used to control, forexample to provide an upgrade to a pre-existing appliance. It is alsopossible to provide a generic sensor which may be configured to operatea range of different appliances. For example, a sensor may be providedthat has programmable keys which a device/appliance provider mayassociate with desired functions by appropriately configuration, forexample by reprogramming.

1. A two-dimensional position sensor comprising a substrate with asensitive area defined by a pattern of electrodes, the pattern ofelectrodes including drive electrodes and sense electrodes generallyextending in a first direction, hereinafter the x-direction, andinterleaved in a second direction, hereinafter the y-direction, whereinthe sense electrodes comprise first, second and third groups of elementsshaped such that adjacent ones of the elements of the first and secondgroups co-extend in the x-direction over a portion of the sensitive areaand adjacent ones of the elements of the second and third groupsco-extend in the x-direction over another portion, and wherein the driveelectrodes are arranged to capacitively couple with the senseelectrodes, wherein the sensor further comprises a controller comprisinga drive unit for applying drive signals to the drive electrodes, and asense unit for measuring sense signals received from each group of thesense electrodes representing a degree of capacitive coupling of thedrive signals between the drive electrodes and each group of the senseelectrodes.
 2. The sensor of claim 1, wherein the controller furthercomprises a processing unit for calculating a position of an interactionwith the sensitive area from an analysis of the sense signals obtainedby applying drive signals to the drive electrodes.
 3. The sensor ofclaim 2, wherein the processing unit is operable to determine positionin the x-direction by an interpolation between sense signals obtainedfrom co-extending pairs of groups of sense electrodes.
 4. The sensor ofclaim 2 or 3, wherein the processing unit is operable to determineposition in the y-direction by an interpolation between sense signalsobtained by sequentially driving the drive electrodes with respectivedrive signals.
 5. The sensor of claim 1, wherein the groups of senseelectrodes which co-extend have complementary tapers over their distanceof co-extension to provide ratiometric capacitive signals.
 6. The sensorof claim 1, wherein the elements of respective groups of senseelectrodes which co-extend have adjacent blocks of varying area overtheir distance of co-extension to provide ratiometric capacitivesignals.
 7. The sensor of claim 1, wherein the drive and senseelectrodes interdigitate in order to provide said capacitive coupling.8. The sensor of claim 7, wherein over the sensitive area the drive andsense electrodes are formed of conductive material which does not exceeda feature width substantially smaller than a characteristic spacing inthe y-direction between adjacent rows of drive electrodes.
 9. The sensorof claim 1, wherein the elements of at least one of the first and thirdgroups of sense electrodes form two sections separated in they-direction by a channel, and wherein the elements of the second groupof sense electrodes are externally connected to the sense unit throughconductive traces that pass through the channels to a side of thesensitive area.
 10. The sensor of claim 1, wherein there are at leastthree groups of sense electrodes externally connected to the sense unitthrough one side of the sensitive area, referred to as peripheral,intermediate and inner sense electrodes, wherein the elements of theinner sense electrodes are externally connected to the sense unitthrough conductive traces which become progressively wider in they-direction from said one side towards the elements of the inner senseelectrodes.
 11. The sensor of claim 1, wherein the elements of at leastone of the groups of sense electrodes are hollow in the plane of thesensitive area.
 12. A method of sensing position of an actuation on asensitive area of a two-dimensional position sensor, the sensitive areabeing defined by a pattern of electrodes including drive electrodes andsense electrodes, both generally extending in a first direction,hereinafter the x-direction, and interleaved in a second direction,hereinafter the y-direction, wherein the sense electrodes comprisefirst, second and third groups of elements shaped such that adjacentones of the elements of the first and second groups co-extend in thex-direction over a portion of the sensitive area and adjacent ones ofthe elements of the second and third groups co-extend in the x-directionover another portion, and wherein the drive electrodes are arranged tocapacitively couple with the sense electrodes, the method comprising:applying drive signals to the drive electrodes; measuring sense signalsreceived from each group of the sense electrodes representing a degreeof capacitive coupling of the drive signals between the drive electrodesand each group of the sense electrodes; determining position in thex-direction by an interpolation between sense signals obtained fromco-extending pairs of groups of sense electrodes; and determiningposition in the y-direction by an interpolation between sense signalsobtained by sequentially driving the drive electrodes with respectivedrive signals.